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Cow Mineral Nutrition: Trace Minerals and Managing Interactions

By Adele Harty
Mineral nutrition is vital to overall cow performance. Without appropriate balance of minerals, cows may not perform as desired or could exhibit detrimental effects. There is value in analyzing your mineral program to determine if modifications need to be made to improve cattle health and performance.
Minerals are divided into two groups based on the quantity of the mineral required by the cow: macro minerals and micro minerals (trace minerals). The macro minerals are required as a percent of the diet dry matter, while micro minerals or trace minerals are required in ppm (parts per million). This article will discuss trace minerals while a previous article discussed macro minerals.
About Trace Minerals
There are six trace minerals of significant importance in a cow’s diet. These are cobalt (Co), copper (Cu), iodine (I), manganese (Mn), selenium (Se) and zinc (Zn). They each play important roles in the body and can have negative impacts if they are deficient or in excess.
The requirement for Co is 0.10 ppm and is typically adequate in summer range and many silages, but can be deficient in low-quality forage (e.g., winter range, crop residue). Cobalt deficiency is characterized by depressed appetite, listlessness, decreased growth, reduced milk production and a rough hair coat.
The cow does not readily absorb Co, but the rumen microbes use it for vitamin B12 synthesis. Vitamin B12 is then used by rumen microbes in metabolic processes to produce propionate, which is a volatile fatty acid that provides energy to the cow.
Copper plays many important roles in the cow’s system, including red-blood cell health, collagen development, reproduction, and immunity. Not only does Cu play important roles by itself, but the combination of Cu, S, and Mo creates several important enzymes involved in nucleotide and vitamin metabolism. The challenge is ensuring that the Cu:Mo ratio is correct and will not cause a negative interaction. This ratio needs to be between 2:1 and 4:1. The cow’s requirement for Mo is very small and frequently met by forages in grazing cattle. There are some areas in western South Dakota that this ratio is reversed and modifications to the mineral supplement program need to be made.
Multiple minerals besides Mo and S can also interact and decrease Cu availability. These include zinc (Zn), iron (Fe), selenium (Se) and phosphorus (P). The forage mineral samples collected over the last three years in the western Dakotas have all been deficient. When this deficiency is coupled with increased levels of the minerals listed above, supplementing adequate levels of Cu becomes more challenging. In addition, soil type can play a role in Cu availability, with alkaline soils reducing that availability. Cattle with a Cu deficiency are characterized as having a lighter colored hair or faded hair coat, reduced conception rates, severe diarrhea, brittle bones and reduced immune response.
The requirement for I is very low (0.5 ppm), however deficiencies are more prevalent than toxicities in the northern United States. Iodine plays a key role in maintaining metabolic rate by producing the hormone thyroxin from the thyroid gland. If I levels are low, thyroxin production is reduced and results in lower metabolic rates, that has a snowball effect on decreasing milk production, weaning weights and overall herd health. Cows that are deficient in I while they are pregnant can have calves that are born blind, weak, hairless or stillborn. Another symptom of deficiency is goiter, an enlargement of the thyroid gland.
Manganese plays an important role in growth and reproduction. The requirement for Mn in growing and finishing cattle is 20 ppm, while the requirement in pregnant and lactating cows is 40 ppm. Cattle have a high tolerance level for Mn, up to 1,000 ppm. However, Mn interacts with other minerals so deficiency effects could be noticed at lower Mn levels.
If Mn requirements are not met, the primary indicator will be reduced conception rates. Other indicators are poor growth rates, low birth weights and increased abortions.
Selenium can be a challenging mineral in South Dakota. In general, west of the Missouri River has adequate Se and some areas have toxic levels, while east of the Missiour River can be deficient. Soil composition drives Se content of forages and the arid regions with more Ca in the soil are more likely to have higher selenium levels. Cattle have a small tolerance range for Se, with 0.10 ppm being the requirement and 5 ppm being toxic. Selenium toxicity is characterized by “blind staggers”, sloughing of hooves and hair, anorexia and a wide range of birth defects. Depending on the situation, a mineral supplement without added Se may be necessary.
Zinc plays a role in immune response, enzyme systems and hoof health. The requirement is 30 ppm and forages, grains and proteins are all sources of Zn. Forages average 20 ppm, grains are approximately 35 ppm, and protein sources average between 60 to 70 ppm Zn. Therefore, if cattle are fed forage based diets, additional Zn supplementation may be necessary.
Signs of Zn deficiency are reduced feed intake and weight gain, excessive salivation, rough hair coat and eventually swelling of the feet and legs.
When it comes to supplementing trace minerals, providing a trace mineralized product that contains Co, I, Cu, Mn and Zn is a good insurance policy for decreasing the occurrence of deficiencies. In certain situations, a trace mineralized salt will be adequate to alleviate mild deficiencies; however, there are other situations when an additional mineral supplement will be necessary to overcome interactions or more extreme deficiencies. Reading the mineral tag and understanding bioavailability of the mineral sources is vital to selecting the appropriate supplement.
The Bottom Line
Mineral nutrition and balance is key to animal performance and productivity. Take time to evaluate your mineral program and determine if the supplements you are using are meeting the needs of your cattle. It is often stated that a mineral supplement is formulated for a region, but there can be significant variations in mineral content of forages from one side of your ranch to the other. It might be valuable for you to sample your forages and water to get a better understanding of what is available to your cows and what they need in a supplement. The final article in this series will address reading the mineral tag and understanding bioavailability of the ingredients in mineral supplements.